Field of the Invention
The technical field of the invention relates to methods for measuring morpho-geometric parameters of a spectacle wearing individual. These parameters may, for example, include the pupillary distance PD, the height H separating the pupil from the lower edge of a lens, the pantoscopic angle ΘP, which is the angle of inclination of the lenses relative to the facial plane of the individual, the distance DLE between the eye and the lens L, and the center of rotation CRO of the eye. Knowledge of these parameters is essential if a pair of spectacles, and in particular a pair of progressive lenses, is to be properly personalized.
Description of Related Art
Methods allowing a certain number of these morpho-geometric parameters to be measured already exist. A first category of these methods employs a large vertical measuring column, with a video camera adjusted to eye height, the spectacle wearing individual looking into a mirror. This type of apparatus is very bulky and therefore requires large premises to carry out the measurements, and it is rather inflexible to use insofar as it cannot easily be moved in order to refine the measurements, nor be dissociated into several elements so as to adapt to a given situation.
A second category of methods involves a smaller apparatus, that can in particular be installed on a table, but that requires a very constraining protocol for measurement and positioning of the spectacle wearing individual. Indeed, this type of method compels the individual to adopt a particular head carriage, and the installation of a clip furnished with a balance-bar on the spectacle frame. A first step then consists in making the individual adopt a natural posture, the balance-bar then being clamped to freeze the angle between the clip and the balance-bar, this angle corresponding to the pantoscopic angle. During a second step, the individual equipped with his spectacle frame and clip, looks at a video camera fixed above a screen. He must incline his head in such a way that the clamped balance-bar is perpendicular to the axis passing through the eyes and the video camera. Such a method demands complex and precise adjustments, and calls for a certain dexterity on the part of the spectacle wearing individual, so as to be able to position himself precisely with respect to the axis of the video camera and to freeze the position of the balance-bar accordingly.